LinkedMarkMail is a simple Linked Data interface for accessing the MarkMail archives. Using its hacky API, the SWAML project offers a RDF version of the information indexed by MarkMail; using SIOC, therefore fully compatible with many other applications.
The alpha services is available at: http://linkedmarkmail.wikier.org/, where you can check both messages and threads by ID (for instance this message or this thread). Futher details at its voID description.
But remember that LinkedMarkMail is free software; so if you'd need it, you can check out its source code:
svn checkout http://svn.berlios.de/svnroot/repos/swaml/trunk/apps/prototypes/linkedmarkmail linkedmarkmail
You can contact with the members of project in the developers mailing list (archives are public). Also, you can report a bug or send a feature request without you need to subscribe of any of project mailing lists.